Vacuum insulation panels are used for the efficient insulation of refrigerators and freezers, insulating transport containers for temperature-sensitive goods, for retrofit insulation in building renovation, etc.
A vacuum insulation panel has in principle a planar core made of open-pored material and an enclosure that surrounds the core on all sides in a close-fitting, complete and gas-tight manner. As a result, it is possible to evacuate the space within the enclosure and consequently to bring the thermal conductivity of the vacuum insulation panels to very low values.
The starting point for the teaching of the present invention is a known vacuum insulation panel (DE 10 2010 019 074 A1), in which the enclosure has at least one gas-tight barrier layer and a sealing layer on the inside of the barrier layer. This vacuum insulation panel comprises a planar core made of an open-pored material, a first barrier film resting on a first main surface of the core over a large area and having at least one sealing layer facing the core, a second barrier film, surrounding the core on its other main surface and likewise having a sealing layer, and a circumferential sealing seam, along which the two barrier films are sealed to one another with the aid of the sealing layers by means of thermal welding.
In the prior art on which the invention is based, it is explained that pressure-loadable materials in the form of powder boards, bulk powders, open-pored foams or glass fiber materials are suitable for the core. In particular, insulating cores made of powder boards or loose powders are conventionally further enclosed by an air-permeable polyester nonwoven in order to reduce the formation of dust, as emerges, for example, from DE 100 585 66 A1. Dust is therefore prevented from being liberated in the vacuum chamber during the evacuation operation and contaminating both the sealing seam and the vacuum chamber.
Core boards made of microporous silica powder have a very fine pore structure and permit relatively high gas pressures without the thermal conductivity of the residual gas playing any part. For example, in these microporous materials, a vacuum of only 1 to 10 mbar is needed to bring the thermal conductivity to 0.004 to 0.005 W/mK. Enclosures made of specific barrier films, which have only an extremely thin, vapor deposited coating of aluminum, ensure that the gas pressure in the core material rises at approximately only one mbar per year.
However, the previous manufacturing processes of vacuum insulation panels with powder filling necessitate a relatively high outlay and cannot be fully automated.
A method which comes relatively close to the demands of automation is described in DE 10 2005 045 726 A1 with the following method steps: a powder is put into a bag made of barrier film; a filter material that is air-permeable but not permeable to powder dust is fixed to the inside of the film bag, close to the opening, in such a way that the interior of the bag is sealed off in a dust-tight manner but air can still escape; the interior is evacuated and finally the bag is closed in the evacuated state.
The fine powder can be retained completely by the filter material applied in the bag opening even in the event of high gas flows in the bag during the evacuation, so that the evacuation space and the sealing seams are not contaminated. However, the method has the disadvantage that the evacuation operation lasts a relatively long time, since the evacuation can be carried out only via the narrow opening equipped with the filter nonwoven and having a relatively low flow cross section. In addition, as a result of the extraction on one side, a rather non-uniform distribution of the powder over the panel surface is produced.
In the first-named known vacuum insulation panel, on the other hand, the manufacture is carried out in a modified way, namely by a planar filter material resting on a second main surface of the core, opposite the first barrier film, over a large area, the second barrier film resting on the outer side of the planar filter material over a large area, and the filter material being welded all around into the sealing seam between the two barrier films.
Since the filter material does not rest just on one end surface of the core but over an entire main surface of the same, the evacuation can take place of the over the entire area of the filter nonwoven, so that a substantially more uniform distribution of the powder over the area is ensured but structures can also deliberately be introduced into the surface, for example steps of defined thickness.
In order to manufacture such a vacuum insulation panel, the loose powder or the powder board can be applied to a first barrier film; the filter material is placed thereon. The filter material is connected to the first barrier film at the edge which follows the later surface form of the vacuum insulation panel, so that a sealed volume is produced for the powder but, nevertheless, is permeable to air and, by virtue of its large area, permits considerably faster evacuation than previously.
In the previously extensively explained prior art, various measures are described for manufacturing vacuum insulation panels of the type under discussion. In particular, it is also explained that the planar core can be built up not only in one piece but also in many parts.
Comprehensive proposals are made for the configuration of the enclosure having the barrier films. Typically achievable gas permeabilities and water vapor permeabilities are described, and proposals are made for the selection of the materials for the barrier layers and the sealing layers.
All the statements in the prior art in this regard are intended also to be used in a corresponding way for the present invention, provided that they do not expressly contradict the following explanations. Thus, for the statements in this regard, full reference is made to the disclosure content of DE 10 2010 019 074 A1.
Vacuum insulation panels of the type under discussion have excellent insulating properties and a completely adequate period of use for many applications. Because of the low thickness of the enclosure, vacuum insulation panels of the type under discussion are delicate to handle, however. Care must be taken that the enclosure of the vacuum insulation panel is not damaged.
During the evacuation of the one-piece or multi-part planar core in the vacuum insulation panel, the air pressure of the surrounding atmosphere occasionally leads to the enclosure being forced non-uniformly into the core. As a result, corrugated surface structures are produced.